This invention relates to a photographic camera system adapted to make a series of exposures at a variable frequency. A particular application of the invention is to an aerial reconnaissance camera system adapted to make a series of exposures at a variable frequency dependent upon the speed and height of an aircraft carrying the camera system. In such a system, it is commonly required for the frequency of the exposures to vary directly with the speed of the aircraft and inversely with the height of the aircraft (above ground). It is known for such an aerial reconnaissance photographic camera system to have a focal plane shutter in the form of a revolvable shutter blind, geared to a film transport system of the camera so that an exposure is made at the correct instant in each cycle. However, in this known camera system, the exposure slit in the shutter blind is of constant width, so that if the cycle time is changed the exposure time is also changed, which is undesirable.